1. Field of the Invention
The present invention relates to a method of processing images photographed by plural cameras and an apparatus for the same, which photographs the surroundings of a vehicle by plural cameras mounted on the vehicle and synthesizes the photographed images to thereby display an image as if one camera positioned above the vehicle photographed the surroundings of the vehicle.
2. Description of the Related Art
When driving a vehicle into a narrow garage or a narrow parking lot, a driver needs to pay close attention, yet the driver still may bring about an accident such as rubbing the vehicle with a surrounding object. When driving the vehicle out of the garage or the parking lot, the driver also needs to pay full attention to surrounding objects and people. Further, there are many other cases that demand the close attention of the driver, for example, when driving the vehicle on a very narrow road or passing an oncoming vehicle in an opposite lane, the driver needs to pay full attention so that the vehicle does not scrape a surrounding object and does not catch a wheel in a gutter.
As a countermeasure, a system broadly applied to vehicles in recent years uses cameras for photographing the surroundings of a vehicle, such as a rear camera that photographs behind the vehicle to display the photographed image on a monitor, so as to facilitate driving the vehicle into a garage or a parking lot, and side cameras that photograph from both sides of the vehicle, so as to confirm vehicles, etc. traveling on the road ahead when the user's vehicle proceeds into an obstructed narrow road. The system monitors the situation surrounding the vehicle, and allows the driver to drive the vehicle while fully comprehending the situation.
However, even though super wide-angle cameras are used as the cameras for photographing the surroundings of the vehicle, when backing the vehicle into a garage in a situation that an obstacle exists near the back of the vehicle, for example, the obstacle leaves the sight of the rear camera as the vehicle backs up, and it becomes impossible to comprehend the state of the obstacle. As a countermeasure for this case, it is conceivable to provide the super wide-angle cameras on both sides of the vehicle, and to make it possible to view an area that is out of sight of the rear camera by means of the side cameras.
However, an image of an object photographed by the above super wide-angle camera provides a large difference between the center and periphery of a photographed image. Viewing only the photographed image will not show a clear positional relation between the object and the vehicle, and the vehicle may encounter an unexpected collision or rubbing. Even if the image by the rear camera is switched to the image by the side cameras, the image of the object such as an obstacle displayed on the screen looks very different from the real object, and it is not easy to comprehend the state of the real object.
To overcome the above problem, there has been a proposal which mounts plural cameras for photographing the surroundings of a vehicle, synthesizes images photographed by these cameras, forms an image as if one camera positioned above the vehicle photographed the vehicle and its surroundings, and displays a synthesized image on a monitor. In using such plural cameras, a construction using four cameras in total, as shown in FIG. 4, for example, has been proposed which includes a left side camera 32 that photographs from the left side of a vehicle 31, a right side camera 33 that photographs from the right side of the vehicle 31, a back side camera 34 that photographs from the back side of the vehicle 31, and a front side camera 35 that photographs from the front side of the vehicle 31. The images photographed by all the cameras are synthesized, and an image as if one camera positioned right above the vehicle 31 photographed the entire surroundings is displayed on a monitor, as FIG. 4(c) illustrates in outline. This system is called the top view system, and the number of cameras for photographing the surroundings of the vehicle is two or three as required, which is appropriately selected, and the cameras are located at various selected positions.
Japanese Patent Laid-Open No. 2004-56219 discloses a technique that provides a marker display on a screen for an object having a ground clearance in an image taken by the rear camera. Japanese Patent Laid-Open No. 2003-204547 discloses a technique that, when photographing the surroundings of the vehicle by using plural cameras and obtaining a synthesized image, sets the photographing directions of the cameras so that the image of an object located in the photographing peripheral region of the plural cameras does not go out of sight.
Adopting the top view system mentioned above, that uses plural cameras for photographing the surroundings of a vehicle, synthesizes images photographed by the cameras, and displays an image as if one camera positioned above the vehicle photographed the surroundings with the vehicle in the center, will provide a display unit that does not give a distorted image of an object near the vehicle, and makes it possible to easily comprehend a feeling of distance and convey a feeling of easy viewing. However, this system cannot photograph a three-dimensional object higher than a setting position of the cameras, or may photograph such an object to be imaged gigantically, which is disadvantageous in the conventional technique.
When a driver slowly backs the vehicle 31 into a garage, as shown in FIG. 5, for example, and when there is an object 36 to the rear of the vehicle 31, a processed display image of the object 36 photographed by the rear camera gives a plane, elongated figure, as shown in FIG. 5(b). Therefore, it is difficult to determine whether the displayed object is planar or not from this displayed image. As a result, when driving the vehicle while viewing this image, the driver will feel uneasy and face a danger of colliding with the object.